Ducting for a fluid transfer pipeline for an aircraft or spacecraft, method for producing same and aeronautical structure incorporating same

ABSTRACT

The present invention relates to a ducting for a fluid transfer pipeline for an aircraft or spacecraft, an aeronautical structure incorporating it and a method for producing this ducting. 
     The ducting ( 1 ) comprises a pipe ( 2 ) with a thermoplastic or thermoplastic elastomeric layer ( 4 ) and a reinforcing layer ( 5 ) surmounting it. The pipe has a curved and/or bent geometry and the reinforcing layer is made of a composite material based on reinforcing means ( 6 ) that are in intimate and direct contact with the subjacent layer, such as the inner layer, said geometry being obtained by one or other of the following two methods (a) and (b):
         a) the inner layer is previously hot formed to give it this geometry, the reinforcing means being of choice:
           (i) impregnated with a thermosetting matrix, the reinforcing layer forming thermosetting composite, or   (ii) either reinforcing fibers intermixed with thermoplastic fibers or powders, or impregnated with a plastic polymeric coating that is curable chemically, the reinforcing layer forming a thermoplastic composite; or   
           b) the inner layer, in its initial rectilinear geometry, is first of all covered with the reinforcing layer in which said reinforcing means are reinforcing fibers intermixed with a thermoplastic material in the form of fibers, film or powder, and this inner layer covered in this way is then blow-molded in order to give the pipe its final geometry, the reinforcing layer obtained forming a thermoplastic composite.

The present invention relates to a bent and/or curved ducting, inparticular for a fluid transfer pipeline for an aircraft or spacecraft,such as a fuel pipeline, mounted in or under the wings of an aircraft,an aeronautical structure incorporating this ducting and a method forproducing same. The invention relates more particularly tothree-dimensional ductings (i.e. of which the axis of symmetry from oneend to the other extends in three dimensions).

Fuel pipelines of current aircraft are usually made of metal (e.g.aluminum, stainless steel or titanium), as are the wings in which theyare housed. Nevertheless, for several years now wings and fuel pipelineshave started to be designed in composite materials, so as to lighten asmuch as possible these pipelines and the wing units incorporating them(e.g. the wing unit, central box section or engine strut) or to reducethe electrical conductivity of these pipelines to prevent risks oflightning strike, notably in the case where these pipes are fixed to thestructures that are themselves composite and are therefore lessconductive than metal.

Reference may be made for example to document WO-A1-2006/136597 for anexample of a composite ducting comprising two coaxial inner and outerconduits separated by struts and that are at least partly made of acomposite thermosetting material, such as an epoxy resin reinforced bycarbon fibers. Mention may also be made of document EP-A1-1 878 562 thatteaches the production of ducting for air-conditioning lines designedfor aircraft, incorporating pipes with thermoplastic or thermosettingplies, for example based on a phenolic resin for the thermosettingmatrix.

Currently, most three-dimensional pipes are made of metal, beingobtained by bending or welding. They are thus relatively heavy, onaccount of the high density of the metallic material used. Compositesthus represent a valuable solution for lightening these pipes, notablyfor the pipes of fuel lines or hydraulic lines or aeronauticalextinguisher lines, where weight is an important factor in performance,economy and the reduction of consumption and emissions.

However, when pipes are made of a composite material with athree-dimensional shape, their production requires:

a rigid mold associated with an inflatable bag of which the role is toapply the wall of the pipe with pressure into the mold, or

a rigid core (of the extractable, fusible or soluble type for example)on which either dried reinforcing fibers are draped that are infusedunder vacuum and then cured in an oven, or prepregs, (i.e. material insheets impregnated with a thermosetting resin of which polymerization isincomplete) that are consolidated and then cured in an autoclave.

A major disadvantage of these known pipes and the methods for producingthem lies in their relatively high cost, since they require costlyequipment (molds and bags in particular) as well as costly cores (caseof extractable cores, for example), cores that have to be replacedregularly after producing several tens of parts (e.g. inflatable bags,flexible mandrels) or even lost cores for each part produced (case ofsoluble or fusible cores).

An object of the present invention is to provide ducting that enablespipelines or tubing to be made with complex three-dimensional shapesthat also overcomes these disadvantages, the ducting having at least onemultilayer pipe comprising a radially inner layer made of thermoplasticmaterial or thermoplastic elastomer that is leakproof and chemicallyresistant to the fluids transported, and at least one reinforcing layersituated radially above the inner layer.

To this end, a ducting according to the invention is such that the pipehas a curved and/or bent, preferably three-dimensional, geometry and maybe complex, and in that the reinforcing layer is made of a compositematerial based on reinforcing means that are preferably fibrous (e,g,carbon, glass or aramid fibers) that are in intimate and direct contactwith the subjacent layer, such as the inner layer, said geometry beingobtained by one or other of the following two methods a) and b):

a) the inner layer is previously hot formed independently of thereinforcing layer so as to pass from an initial rectilinear geometry tothis curved and/or bent geometry, said reinforcing means being ofchoice:

-   -   (i) impregnated with a thermosetting matrix, the reinforcing        layer forming a thermosetting composite with a thermosetting        matrix having a curing temperature less than the melting point        of said subjacent layer, or    -   (ii) either the reinforcing fibers are intermixed with        thermoplastic fibers or powders, or are impregnated with a        plastic polymeric coating that is curable chemically, the        reinforcing layer forming in both these cases a thermoplastic        composite with a thermoplastic matrix having a transformation        temperature less than that of said subjacent layer; or

b) the inner layer, in its initial rectilinear geometry, is first of allcovered with the reinforcing layer in which said reinforcing means arereinforcing fibers intermixed with a thermoplastic material in the formof fibers, a film or powder, and this inner layer covered in this way isthen blow-molded after being softened in order to give the pipe itscurved and/or bent geometry, the reinforcing layer obtained forming acomposite with a thermoplastic matrix.

It will be noted in a general manner that the ducting according to theinvention, whether it be obtained by method a) or b), is such that itsinner layer is functional both for its function of resistance to thefluid transported as well as for direct application of the reinforcinglayer by intimate contact (e.g. by bag molding or drape-forming). Aswill be given in detail in the remainder of the present description,this inner layer is not only intimately connected to the remainder ofthe pipe, but additionally acts in its production by forming a core forthe in situ application of this reinforcing layer.

With reference to alternative (i) of method a), it will be noted thatthe essential value of this thermoplastic/thermosetting hybrid structureconsists of being able to cure the thermosetting matrix of thereinforcing layer without causing the inner layer to melt. For example,an epoxy resin may be cured quite rapidly at temperatures close to 140°C. on a thermoplastic inner layer of which the melting point is forexample above 170° C. (case of a polyamide).

With reference to method b), it will be noted that the composite with athermoplastic matrix that is formed by the corresponding reinforcinglayer, may be such that this matrix has a transformation temperaturevarying within a wide range that may for example be close to that of thesubjacent layer, such as the inner layer. This method b) thus has,compared with method a), the advantage of not involving a limitation tothe transformation temperature of the matrix used. Another advantage ofthis method b) is that it is possible, by means of the blow-moldingemployed for obtaining the bent and/or curved geometry, to consolidatethe thermoplastic matrix even better, to the point where it is given thepolished mirror appearance of the mold.

An important advantage of this invention will also be noted, which isthat regulation of the mechanical properties, for example the resistanceto pressure/reduced pressure or rigidity of the pipe, may be achieved byadjusting the number and thickness of the reinforcing means chosen butalso by placing reinforcements in very precise places in the form oflocalized sleeves.

Advantageously, said reinforcing means may be of the fibrous type, beingpreferably chosen from the group consisting of one or more braids, oneor more knitted fabrics, one or more fabric plies, unidirectionalribbons or webs, complexes of the type with a non-woven core either sideof which mats or fabrics are sewn or knitted (e.g. with the trade name“Rovicore”), complexes based on thermosetting reinforcements (e.g. withthe trade name “Injectex”) and combinations of these reinforcing means,for example with a damping material such as an elastomer.

Even more advantageously, said reinforcing means may comprise one ormore cylindrical braids optionally separated from each other by layersdamping vibrations, the or each braid being preferably made of carbon oraramid for their lightness.

Also advantageously, the braiding angle that the or each braid makeswith the axis of symmetry of the pipe, will be substantially equal to54° on at least one portion of the pipe, so as to prevent flow withtemperature of the subjacent layer, such as the inner layer or thethermoplastic matrix of the reinforcing layer, and to maintain thisbraid in equilibrium on these layers when they are put under pressure.It will however be noted that this braiding angle may vary within moreor less large proportions around 54° along the pipe, notably at thelocation of changes in radius (e.g. bends or curved portions) andpossible changes in pipe diameter.

Preferably, the inner layer is based on at least one thermoplasticpolymer chosen from the group consisting of polyamides (PA),polyetherimides (PEI), phenylene polysulfides (PPS),polyetheretherketones (PEEK), polyetherketoneketones (PEKK) and mixturesthereof.

In a more preferred manner, the inner layer is based on at least onepolyamide consisting of PA6, PA6.6, PA11, PA12 and mixtures thereof,that has a low glass transition temperature Tg, for example close to 45°C. (above which the polyamide is subject to flow), said braiding angleof 54° preventing this inner layer from flowing with temperature athigher temperatures of use. In point of fact, this angle makes itpossible to use these very low cost thermoplastic polymers of which theTg temperature is situated below the maximum temperatures of use, whiletheir melting point is above for example 170° C., without the risk offlow, even when used continuously at 100° C. for example, by virtue ofthe dimensional blocking of the inner layer by the reinforcing means.

As a variant, the inner layer may be based on at least one thermoplasticelastomer, preferably an alloy of thermoplastic vulcanizates (TPV).

The material of the inner layer is of course equally chosen for its goodadhesion to the thermosetting matrix used for consolidating thereinforcing means within the reinforcing layer.

It will be noted that if the thermosetting resins (e.g. epoxy resins,bismaleimides (BMI), phenolics, polyesters, vinylesters andpolyetherimides (PEI)) can at the limit be used in the inner layer, thelatter is advantageously made of a thermoplastic polymer or athermoplastic elastomer, since these polymers have:

better chemical resistance to the fluids conveyed,

better leakproofness even at very low thicknesses (between 0.3 and 1mm),

greater lightness (density often equal to 1 instead of around 1.5 forthermosetting resins),

better impact resistance, and

ease of extrusion and therefore reduced cost.

According to a preferred embodiment of the invention, the reinforcingmeans of the reinforcing layer are directly drape-formed or bag-moldedon the inner layer which then forms a functional drape-forming core.

According to another embodiment of the invention, the pipe includes,radially between the inner layer and the adjacent reinforcing layer, atleast one intermediate layer with the electrical conductivity adjusted,for example provided so as to reduce the overall electrical conductivityof the pipe as regards the risk of lightning strike and of explosion ofthe fluid conveyed, or conversely to increase it, for example as regardsthe requirement for electrostatically discharging fluid passing throughthe pipe, said reinforcing means of the reinforcing layer being directlydrape-formed over the subjacent intermediate layer.

With reference to alternative (i) of method a) according to theinvention, the reinforcing means that are included in the reinforcinglayer are advantageously directly drape-formed or bag-molded over thesubjacent layer, such as the inner layer.

According to a first example of the invention, these reinforcing meansare advantageously drape-formed dry and infused under vacuum with saidthermosetting matrix overmolded in the viscous liquid state, by a methodknown as infusion. In this case, the inner layer may advantageously bebased on at least one polyamide chosen from the group consisting of PA6,PA6.6, PA11, PA12 and mixtures thereof for example, this inner layerhaving a minimized thickness in relation to the pressure reduction usedfor this vacuum infusion (relative pressure less than or equal to 1bar). In point of fact, this thickness may advantageously be distinctlyless than 1 mm for an inner layer made of non-reinforced PA6, 6.6, 11 or12, 50 mm in diameter for example. Thus, the pipe obtained may beparticularly light, due to the smallest thickness required for this towithstand a pressure of several bars in an autoclave.

According to this first example, these reinforcing means are preferablyinfused under vacuum with a liquid thermosetting resin chosen from thegroup consisting of epoxy, bismaleimide, phenolic, polyester,vinylester, polyetherimide resins and mixtures thereof. Even morepreferably, the reinforcing layer forms a thermosetting epoxyresin/carbon composite or epoxy/aramid or epoxy/glass composite, beingfor example formed of one or more braids made of carbon or aramid orglass infused with an epoxy resin, for example.

In relation to this first example, it will be noted that the inner layerforms a core both for the drape-forming and infusion of thesereinforcing means.

It will also be noted that these reinforcing means, such as one or morebraids, which are drape-formed dry over the subjacent layer, such as theinner layer, thus easily take up the radii of curvature of thispreviously curved, molded and/or bent layer.

It will also be noted that, for fuel pipelines where electric arcs mustbe prevented that may cause explosions, the thermoplastic material orthermoplastic elastomer of the inner layer may be made conducting, forexample by adding fillers (e.g. carbon black, graphite, etc) orconducting fibers (e.g. short, long or continuous carbon fibers) so asto evacuate electrostatic charges generated by movements of fluid insidethe pipe.

Similarly, overlapping conductive reinforcements, such as braids, couldbe added during infusion so as to enable electrostatic charges to be ledtowards the fixing supports or neighboring structures without causingarcing to these structures.

According to a second example of the invention, these reinforcing meansare advantageously pre-impregnated with said thermosetting matrix,consolidated in contact with the subjacent layer of the pipe and thencured. It will however be noted that this pre-impregnation has therelative disadvantage of involving higher cost than that inherent in theinfusion technique.

With reference to alternative (ii) of method a) according to theinvention, the reinforcing layer and the reinforcing means that areincluded therein may be formed:

either of a continuous composite element such as a strip that containssaid reinforcing fibers intermixed with said thermoplastic fibers orpowders, and which is wound around the inner layer,

or of one or more braids impregnated with said plastic polymericcoating, cured chemically, preferably by reaction injection molding“RIM” for example based on a polyurethane (these braids being forexample made of carbon fibers).

It will be noted that the transformation temperature of thethermoplastic matrix that is chosen to be less than that of the innersubjacent layer, prevents any deformation or changes to the geometry orproperties of this inner layer during consolidation of the reinforcinglayer that is performed above its melting point. The thermoplasticmatrix or curable oligomers may be in a liquid form so that they can beinfused, or may be used in any other impregnating method permittingcompacting and curing at very low pressures.

With reference to method b) according to the invention, said reinforcingfibers, such as carbon, glass or aramid fibers, are intermixed with saidthermoplastic material to form the reinforcing layer that isdrape-formed or bag-molded over the subjacent layer, such as the innerlayer.

Advantageously, the pipe may optionally include an outer sheath definingits radially outer surface, this sheath being for example designed toimprove the physical properties and chemical resistance of the pipeand/or to damp vibrations received and/or to ensure electricalinsulation and/or thermal insulation and/or to improve the impactresistance of the pipe.

According to another feature of the invention, the ducting may includeflanges for connecting the pipe to the remainder of the pipeline, eachflange being made of a metallic, thermoplastic or compositethermoplastic material and being integrated with said reinforcing meanswhile partially covering the latter by direct overmolding at one end ofthe pipe, so that these reinforcing means ensure the continuity of theducting to mechanical forces.

These reinforcing means may then be gripped on their two radially innerand outer faces by two collars that each flange carries, and are securedto these collars during infusion by said thermosetting matrix overmoldedon these reinforcing means, with reference to alternative (i) of step a)according to the invention. Each free end of these reinforcing means,such as a braid, is in this way intimately bonded to the correspondingflange during this single infusion operation, in this way conferringmaximum mechanical strength to the pipe provided with flanges.

Preferably, each flange may be made of a thermoplastic or compositethermoplastic material and is shrunk-on or rotation welded onto theradially inner face of the inner layer of the pipe. It will be notedthat this shrinking-on may be facilitated by the thermoplasticelastomeric nature of the inner layer, and as a variant, these flangesmay be fixed by adhesive, gripped or shrunk-on, since the thermoplastichas the advantage of remaining deformable, contrary to a thermoset.

Equally preferably, each flange may contain electrically conductiveinserts, for example metallic, or of the conductive braid type, on whichit is overmolded, so as to obtain a specific electrical conductivity forthe ducting that is made in this way more or less conducting orinsulating, or so as to be able to connect it to adjacent structures(grounding).

The flanges may be filled or not with fibers or fillers that may haveseveral functions:

for reinforcement: short or long fibers, and

for electrical conductivity: various fillers may be incorporated inthese flanges to adjust their conductivity.

In addition, the form and inner contacts of the flanges may also make itpossible to ensure electrical equipotentiality between the inside andoutside of the pipe.

An aeronautical structure according to the invention (e.g. an aircraftwing) that contains fluid transfer pipelines (e.g. hydraulic pipelinesfor fuel, oils or extinguisher fluids) is characterized in that one ormore ducts of at least one of these pipelines is as defined above.

A method according to the invention for producing ducting as definedabove substantially comprises the following successive steps:

A) forming the thermoplastic or thermoplastic elastomeric inner layer(filled or not) preferably by extrusion, with optional deposition of atleast one intermediate layer on this inner layer, so as to obtain ablank with a geometry that is either rectilinear, curved and/or bent(preferably three-dimensional),

B) bag molding or drape-forming in situ said reinforcing means directlyonto this blank, which constitutes in this way a functional core for bagmolding or drape-forming,

C) consolidation in situ of these reinforcing means in contact with thiscore by a thermosetting or thermoplastic matrix with optionally, only inthe case where step B) is carried out on a blank with rectilineargeometry, blow-molding the rectilinear core softened by preheatingfollowing this step B) so as to obtain a multilayer structure withcurved and/or bent geometry, then

D) curing and/or cooling this multilayer structure so as to obtain thecurved and/or bent pipe with a composite reinforcing layer.

With reference to the aforementioned method a) according to theinvention, the blank formed in step A), initially with a rectilineargeometry, is subjected to hot forming so as to obtain, in view of stepB), a core designed for bag molding or drape-forming that is previouslycurved and/or bent with a preferably three-dimensional geometry.

This hot forming may be carried out:

either by locally heating the blank for bending before preheating,

or by heating all the blank to a predetermined temperature enabling itto be softened and by blow-molding or by thermoforming in a mold under avery low internal pressure and without an inflatable bag since it is thetube itself, formed in this way, that takes its place.

It will be noted that this hot forming only requires very low forces orpressures, by virtue of the softening of the previously heatedthermoplastic or thermoplastic elastomeric blank and makes it possibleto dispense with any other inner core.

With reference to alternative (i) of the aforementioned method a), stepsB) and C) are put into practice by drape-forming the reinforcing means,such as one or more braids, for example made of carbon, on the curvedand/or bent core formed in A), with:

either dry drape-forming of the reinforcing means followed by infusionof these under vacuum in step C) by means of said thermosetting matrixovermolded in the liquid state, such as an epoxy resin, this coreconstituting in this way a functional core for drape-forming andinfusion,

or the use, for this drape-forming, of a prepreg that is consolidated incontact with the core in step C).

The principle of the invention thus consists of separating theproduction of the inner layer from that of the outer reinforcing layerand, according to this alternative (i) of method a), of making use ofthis previously formed inner layer as a core for drape-forming andinfusion during production of the reinforcement. In a general manner,with reference to methods a) and b) of the invention, the innerfunctional tube provides in both cases the role of mandrel or support onwhich the reinforcing layer is produced. It ensures chemical resistanceand leakproofness to fluids inside the pipe, and also enables theinternal conductivity of the pipe finally obtained to be adjusted.

Even more advantageously for this alternative (i), it is chosen toemploy this dry drape-forming followed by infusion, using a flexiblesheet or vacuum bag for this.

With reference to alternative (ii) of method a) according to theinvention, steps B) and C) are put into practice:

either by winding around the core a continuous composite element such asa thread or strip that contains said reinforcing fibers intermixed withsaid thermoplastic fibers or powders,

or by impregnating said reinforcing means by means of said plasticpolymeric coating that can be chemically cured, preferably by molding ofthe “RIM” reaction type, for example by means of a polyurethane.

With reference to method b) according to the invention, step B) is putinto practice directly on a blank with a rectilinear geometry obtainedin step A), without hot-forming this blank.

As previously indicated, the inner layer is then first of all formed toan initial rectilinear geometry (i.e. neither curved nor bent), whichhas the advantage of reducing the production method for the pipe. Thisinner layer of the reinforcing layer is then covered with a fibrousmaterial (for example by drape-forming, “bandaging” or bag molding witha preform or a braid) intermixed as it is with reinforcing fibers (e.g.carbon, glass or aramid) o with a thermoplastic material formed of otherfibers, a film or a powder. The structure obtained in this way ispreheated to its softening temperature and is placed in a mold (of whichthe cavity has a diameter slightly greater than that of the structure)where it is subjected to blow-molding in order to give it the desiredcurved and/or bent geometry.

It will be noted that the tube formed by the inner layer does not, underthese conditions, exhibit the slightest risk of collapsing on account ofits being under pressure, while this risk, although low, exists withmethod a) according to the invention that calls for a reduction inpressure for the consolidation step.

As regards the curing step D), this is carried out under vacuum in anoven, i.e. without having to use an autoclave or other complexequipment.

In a general manner, it will be noted that this method according theinvention enables an easy addition to be made:

of local reinforcement (e.g. braids, fabrics, unidirectional strips,knitted fabrics) in the reinforcing layer without affecting theproduction equipment used,

of a damping intermediate layer, preferably placed between two fibrousreinforcements so as to damp any vibratory modes of the pipes (cf. forexample excitation by windmilling with aircraft that have lost a bladeon a jet engine), and

of added end flanges.

According to another feature of the invention, this production methodmay additionally include the securing in step C) of connecting flangesof the pipe to the reinforcing means, so that each flange at leastpartially covers the latter at one end of the pipe, so that thesereinforcing means ensure the mechanical continuity of the ducting.

Advantageously, this securing is achieved by overmolding saidthermosetting matrix involved in the infusion in the case of alternative(i) of method a), while gripping the reinforcing means on their tworadially inner and outer faces with two collars, each of which has aflange.

The infusion operation may thus also serve to overmold these end flangesdirectly on the pipe, while ensuring continuity to mechanical forceswith the drape-formed reinforcing means.

Also advantageously, each flange is shrunk-on or rotation welded orwelded by ultrasound on the radially inner face of the inner layer ofthe pipe, this flange then being preferably made of a thermoplasticmaterial or composite thermoplastic.

It will be noted that the ends of the inner core (i.e. typically of theinner layer) may be previously thermoformed in order to facilitateassembly of the flanges.

Other features, advantages and details of the present invention willbecome apparent on reading the following description of variousembodiments of the invention, given as non-limiting examples, saiddescription being made with reference to the appended drawings, inwhich:

FIG. 1 is a drawing showing, in perspective, a three-dimensional ductingaccording to the invention,

FIG. 2 is a drawing showing, in perspective, a braid in the unrolledstate, that may be used as a reinforcing means in the reinforcing layerof this ducting according to the invention, and

FIG. 3 is a partial schematic view in axial section of a ducting formedof a pipe provided with connecting flanges, according to an example ofan embodiment of the invention.

As may be seen in FIG. 3, a ducting 1 according to the invention, whichcomprises a pipe 2, at the ends of which flanges 3 are connected, issuch that the pipe 2 substantially comprises:

a radially inner layer 4 made of a thermoplastic material orthermoplastic elastomer (preferably made of polyamide) that is leakproofand chemically resistant to the fluid transported (for example fuel)this layer being for example hot-formed independently of the reinforcinglayer 5 that it is designed to receive in the case of method a)according to the invention, so as to give the pipe a preferablythree-dimensional curved and/or bent geometry, as may be seen in FIG. 1,and

the reinforcing layer 5 that surmounts the inner layer 4 (as previouslyindicated, one or more intermediate layers could be inserted radiallybetween these layers 4 and 5) and that is made of a composite materialbased on the reinforcing means 6 (such as one or more carbon braids—seeFIG. 2—preferably braided at an angle of approximately 54° is over atleast part of its length so as to hold this layer 5) directlydrape-formed over this layer 4, in equilibrium under pressure.

More precisely, and still in the example of method a) according to theinvention, these reinforcing means 6 are of choice:

(i) impregnated with a thermosetting matrix, the layer 5 forming athermosetting composite, or

(ii) either reinforcing fibers intermixed with thermoplastic fibers orpowders, or fibers impregnated with a plastic polymeric coating that maybe chemically cured, preferable by “RIM” reaction-type molding, forexample based on a polyurethane, the reinforcing layer forming athermoplastic composite.

Preferably, these reinforcing means 6 according to method a) are drydrape-formed over the layer 4 and then infused under vacuum in contacttherewith, by means of a flexible vacuum sheet, with a thermosettingresin overmolded in the liquid state, as for example, in a non-limitingmanner, an epoxy resin. In this way, the layer 4 forms a core both forthe drape-forming and infusion of these reinforcing means 6. Thestructure obtained is then cured in an oven under vacuum.

As illustrated in FIG. 3, the connecting flanges 3 of the pipe 2 may beadvantageously secured to the drape-formed reinforcing means 6 (e.g. thebraid or braids) so that each flange partially covers the reinforcingmeans 6 at one end 5 a of the layer 5 while being closely bonded to thelatter. According to the invention, this securing is achieved byovermolding with the liquid thermosetting resin used during infusion,while gripping the end 5 a of the reinforcing means 6 by two radiallyouter and inner collars 3 a and 3 b, each of which has a flange 3.

Each flange 3 may also be shrunk-on or rotation welded (i.e. byfriction) in the preferred case where it is made of a thermoplasticmaterial or composite thermoplastic, onto the radially inner face of theinner layer 4 of the pipe 2, via an inner portion 3 c of this flange 3.

In this way, the reinforcing means 6 thus consolidated with resin,ensure, after this is cured, the mechanical continuity of the ducting 1to the forces of which it is the source in use.

As previously explained with reference to method b) according to theinvention, it is also possible to cover the inner layer 4 directly, inits initial rectilinear geometry, with the reinforcing layer 5, wherethe reinforcing means 6 are reinforcing fibers intermixed with athermoplastic material (equally in the form of fibers, films or powder)and then to give the previously softened structure its final curvedand/or bent geometry by a blow-molding technique in a suitable mold.

1) Ducting (1), in particular for a fluid transfer pipeline for anaircraft or spacecraft, such as a fuel pipeline mounted in or under eachof the wings of an aircraft, the ducting having at least one multilayerpipe (2) comprising a radially inner layer (4) made of thermoplasticmaterial or thermoplastic elastomer that is leakproof and chemicallyresistant to the fluid transported, and at least one reinforcing layer(5) situated radially above the inner layer, characterized in that thepipe has a curved and/or bent, preferably three-dimensional geometry,and in that the reinforcing layer is made of a composite material basedon reinforcing means (6) that are in intimate and direct contact withthe subjacent layer, such as the inner layer, said geometry beingobtained by one or other of the following two methods a) and b): a) theinner layer is previously hot formed independently of the reinforcinglayer so as to pass from an initial rectilinear geometry to this curvedand/or bent geometry, said reinforcing means being of choice: (i)impregnated with a thermosetting matrix, the reinforcing layer forming athermosetting composite with a thermosetting matrix having a curingtemperature lower than the melting point of said subjacent layer, or(ii) either reinforcing fibers intermixed with thermoplastic fibers orpowders, or impregnated with a plastic polymeric coating that is curablechemically, the reinforcing layer forming in both these cases athermoplastic composite with a thermoplastic matrix having atransformation temperature less than that of said subjacent layer; or b)the inner layer, in its initial rectilinear geometry, is first of allcovered with the reinforcing layer in which said reinforcing means arereinforcing fibers intermixed with a thermoplastic material in the formof fibers, film or powder, and this inner layer covered in this way isthen blow-molded after being softened in order to give the pipe itscurved and/or bent geometry, the reinforcing layer obtained forming acomposite with a thermoplastic matrix. 2) Ducting (1) according to claim1, characterized in that said reinforcing means (6) are of the fibroustype, being chosen from the group consisting of one or more braids, oneor more knitted fabrics, one or more fabric plies, unidirectionalstrips, complexes of the type with a non-woven core either side of whichmats or fabrics are sewn or knitted, complexes based on thermosettingreinforcing fibers and combinations of these reinforcing means, forexample with a damping material such as an elastomer. 3) Ducting (1)according to claim 2, characterized in that said reinforcing means (6)comprise one or more cylindrical braids optionally separated from eachother by layers damping vibrations, the or each braid being preferablymade of carbon. 4) Ducting (1) according to claim 3, characterized inthat the braiding angle that the or each braid (6) makes with the axisof symmetry (X) of the pipe (2), is substantially equal to 54° on atleast one portion of the pipe, so as to prevent flow with temperature ofthe subjacent layer, such as the inner layer (4) or the thermoplasticmatrix of the reinforcing layer, and to maintain this braid inequilibrium on these layers when they are put under pressure. 5) Ducting(1) as claimed in one of the preceding claims, characterized in that theinner layer (4) is based on at least one thermoplastic polymer chosenfrom the group consisting of polyamides (PA), polyetherimides (PEI),phenylene polysulfides (PPS), polyetheretherketones (PEEK),polyetherketoneketones (PEKK) and mixtures thereof. 6) Ducting (1)according to claims 4 and 5, characterized in that the inner layer (4)is based on at least one polyamide that is chosen from the groupconsisting of PA6, PA6.6, PA11, PA12 and mixtures thereof, and that hasa low glass transition temperature Tg, for example close to 45° C., saidbraiding angle preventing this inner layer from flowing at highertemperatures of use. 7) Ducting (1) according to claim 3 or 4,characterized in that the inner layer (4) is based on at least onethermoplastic elastomer, preferably an alloy of thermoplasticvulcanizates (TPV). 8) Ducting (1) as claimed in one of the precedingclaims, characterized in that said reinforcing means (6) of thereinforcing layer (5) are directly drape-formed or bag-molded on theinner layer (4), which forms a functional drape-forming core. 9) Ducting(1) as claimed in one of claims 1 to 7, characterized in that the pipe(2) includes, radially between the inner layer (4) and the adjacentreinforcing layer (5), at least one intermediate layer with theelectrical conductivity adjusted, for example provided so as to reducethe overall electrical conductivity of the pipe as regards the risk oflightning strike and of explosion of the fluid conveyed, saidreinforcing means of the reinforcing layer being directly drape-formedover the subjacent intermediate layer. 10) Ducting (1) as claimed in oneof the preceding claims, characterized in that the reinforcing layer (5)and said reinforcing means (6) that are included therein are as definedin alternative (i) of method a), these latter being directlydrape-formed or bag-molded over the subjacent layer, such as the innerlayer (4). 11) Ducting (1) according to claim 10, characterized in thatsaid reinforcing means (6) are drape-formed and infused under vacuum bymeans of said thermosetting matrix overmolded in the liquid state. 12)Ducting (1) according to claim 11, characterized in that the inner layer(4) is based on at least one polyamide chosen from the group consistingof PA6, PA6.6, PA11, PA12 and mixtures thereof, this inner layer havinga minimized thickness in relation to the pressure reduction used forthis vacuum infusion. 13) Ducting (1) according to claim 11 or 12,characterized in that said reinforcing means (6) are infused undervacuum by means of a thermosetting liquid resin chosen from the groupconsisting of epoxy resins, bismaleimides (BMI), phenolics, polyesters,vinylesters and polyetherimides (PEI) and mixture thereof. 14) Ducting(1) according to claim 13, characterized in that the reinforcing layer(5) forms a thermosetting composite of epoxy resin/carbon orepoxy/aramid or epoxy/glass, being preferably formed of one or morebraids (6) made of carbon infused with an epoxy resin. 15) Ducting (1)according to claim 8 and as claimed in one of claims 11 to 14,characterized in that the inner layer (4) forms a core both fordrape-forming and infusion of said reinforcing means (6). 16) Ducting(1) according to claim 10, characterized in that said reinforcing means(6) are pre-impregnated with said thermosetting matrix, consolidated incontact with the subjacent layer (4) of the pipe (2) and then cured. 17)Ducting (1) as claimed in one of claims 1 to 9, characterized in thatthe reinforcing layer (5) and the reinforcing means (6) that areincluded therein are as defined in alternative (ii) of method a), thisreinforcing layer being formed: either of a continuous composite elementsuch as a strip that contains said reinforcing fibers intermixed withsaid thermoplastic fibers or powders, and which is wound around theinner layer (4), or of one or more braids impregnated with said plasticpolymeric coating, cured chemically, preferably by reaction injectionmolding “RIM” for example based on a polyurethane. 18) Ducting (1) asclaimed in one of claims 1 to 9, characterized in that the pipe (2) isobtained by method b), said reinforcing fibers (6), such as carbon,glass or aramid fibers, being intermixed with said thermoplasticmaterial to form the reinforcing layer (5) that is drape-formed orbag-molded over the subjacent layer, such as the inner layer (4), itbeing possible for the thermoplastic matrix of this reinforcing layerthen to have a transformation temperature close to that of thissubjacent layer. 19) Ducting (1) as claimed in one of the precedingclaims, characterized in that it incorporates flanges (3) for connectingthe pipe (2) to the remainder of the pipeline, each flange being made ofa metallic, thermoplastic or composite thermoplastic material and beingsecured to said reinforcing means (6) while partially covering thelatter at one end (5 a) of the pipe, so that these reinforcing meansensure the continuity of the ducting to mechanical forces. 20) Ducting(1) as claimed in one of claims 11 to 15 and according to claim 19,characterized in that said reinforcing means (6) are gripped on theirtwo radially inner and outer faces by two collars (3 a and 3 b) thateach flange (3) carries, and are secured to these collars duringinfusion by said thermosetting matrix overmolded on these reinforcingmeans. 21) Ducting (1) according to claim 19 or 20, characterized inthat each flange (3) is made of a thermoplastic or compositethermoplastic material and is shrunk-on or rotation welded or welded byultrasound onto the radially inner face of the inner layer (4) of thepipe (2). 22) Ducting (1) according to claim 21, characterized in thateach flange (3) contains electrically conductive inserts, for examplemetallic, or of the conductive braid type, on which it is overmolded, soas to obtain a specific electrical conductivity for the ducting or so asto be able to connect it to adjacent structures. 23) Ducting (1) asclaimed in one of the preceding claims, characterized in that said pipe(2) includes an outer sheath defining its radially outer surface, thissheath being for example designed to improve the physical properties andchemical resistance of the pipe and/or to damp vibrations receivedand/or to ensure electrical insulation and/or thermal insulation and/orto improve the impact resistance of the pipe. 24) Aeronautical structurecontaining fluid transfer pipelines, characterized in that one or moreductings (1) of at least one of these pipelines is as defined in one ofthe preceding claims. 25) Method for producing a ducting (1) as claimedin one of claims 1 to 23, characterized in that it substantiallycomprises the following successive steps: A) forming the thermoplasticor thermoplastic elastomeric inner layer (4) preferably by extrusion,with optional deposition of at least one intermediate layer on thisinner layer, so as to obtain a blank with a geometry that is eitherrectilinear, curved and/or bent, B) bag molding or drape-forming in situsaid reinforcing means directly onto this blank, which constitutes inthis way a functional core for bag molding or drape-forming, C)consolidation in situ of these reinforcing means in contact with thiscore by a thermosetting or thermoplastic matrix with optionally, only inthe case where step B) is carried out on a blank with rectilineargeometry, blow-molding the rectilinear core softened by preheatingfollowing this step B) so as to obtain a multilayer structure withcurved and/or bent geometry, then D) curing and/or cooling thismultilayer structure so as to obtain the curved and/or bent pipe (2)with a composite reinforcing layer (5). 26) Method according to claim25, characterized in that the blank formed in step A), initially with arectilinear geometry, is subjected to hot forming so as to obtain, inview of step B), a core (4) designed for bag molding or drape-formingthat is previously curved and/or bent with a preferablythree-dimensional geometry. 27) Method according to claim 26,characterized in that this hot forming is carried out: either by locallyheating the blank for bending with preheating, or by heating all theblank to a predetermined temperature enabling it to be softened and byblow-molding or by thermoforming in a mold under a very low internalpressure and without an inflatable bag. 28) Method according to claim 26or 27, characterized in that steps B) et C), according to (i), are putinto practice by drape-forming said reinforcing means (6), such as oneor more braids, for example made of carbon, on the curved and/or bentcore (4) formed in A), with: either dry drape-forming of the reinforcingmeans in step B) followed by infusion of these under vacuum in step C)by means of said thermosetting matrix overmolded in the liquid state,such as an epoxy resin, this core constituting in this way a functionalcore for drape-forming and infusion, or the use for this drape-formingof a prepreg that is consolidated in contact with the core in step C).29) Method according to claim 28, characterized in that this drydrape-forming is carried out followed by infusion using a flexible sheetor vacuum bag. 30) Method according to claim 26 or 27, characterized inthat steps B) and C), according to alternative (ii), are put intopractice: either by winding around the core (4) a continuous compositeelement such as a thread or strip that contains said reinforcing fibersintermixed with said thermoplastic fibers or powders, or by impregnatingsaid reinforcing means by means (6) of said plastic polymeric coatingthat can be chemically cured, preferably by molding of the “RIM”reaction type, for example by means of a polyurethane. 31) Methodaccording to claim 25, characterized in that step B) is put intopractice directly on a blank with a rectilinear geometry obtained instep A), without hot-forming this blank. 32) Method as claimed in one ofclaims 25 to 31, characterized in that the curing step D) is carried outunder vacuum in an oven. 33) Method as claimed in one of claims 26 to30, characterized in that it additionally includes the securing in stepC) of the connecting flanges (3) of the pipe (2) to said reinforcingmeans (6) so that each flange partially covers the latter at one end (5a) of the pipe, so that these reinforcing means ensure the mechanicalcontinuity of the ducting. 34) Method according to claims 29 and 33,characterized in that this securing is achieved by overmolding saidthermosetting matrix involved in the infusion while gripping saidreinforcing means (6) on their two radially inner and outer faces withtwo collars (3 a and 3 b), each of which has a flange (3). 35) Methodaccording to claim 33 or 34, characterized in that each flange (3), thatis preferably made of a thermoplastic or composite thermoplasticmaterial, is shrunk-on or rotation welded or welded by ultrasound ontothe radially inner face of the inner layer (4) of the pipe (2).